1. Field of the Invention
The present invention relates to a media converter for connecting from one type of transmission media to another, in particular to a control technique of the media converter and a failure detection technique in a network using media converters.
2. Description of the Related Art
There has been a lot of talk recently about FTTH (Fiber To The Home) allowing high-speed transmission of multimedia data such as music, moving picture, and medical data by the installation of optical fiber directly to the home. In an era of FTTH, a media converter is an indispensable communication device to connect a fiber-optic line to a computer in the home or office.
In general, a media converter has a pair of ports that are to be connected to a fiber-optic cable and a UTP cable, respectively. For each of the ports, a physical-layer device is provided, which supports MII (Media Independent Interface) conforming to IEEE802.3 standards.
In addition, it usually has a missing-link function such that, in case of disconnection in one link, the other link is automatically disconnected. For example, in the event that the link on the fiber-optic side has been disconnected due to some failure on the fiber-optic cable, the media converter automatically disconnects the other link on the UTP cable side.
In the case where such a media converter is used to connect the UTP cable to the fiber-optic cable, it is necessary to perform a link test to check whether each cable is properly connected to an opposite device on a corresponding link. A conventional media converter is provided with a link-test switch by which a link test function is activated to determine whether each link is properly established. The link status for each port is indicated by a light-emitting diode (LED) provided for each port.
There have been proposed various link test techniques of networks. For example, Japanese Patent Application Unexamined Publication No. 8-331126 discloses a link test method using a special control code. A switch transmits the special control code to another switch that is the opposite end of the link. The other switch, when receiving the control code, sends a response to the control code back to the source switch. The source switch analyzes the response message or detects the presence or absence of a response to determine whether the network link normally functions or not.
However, the above link test technique is designed to test a link between network switches and is fundamentally different in structure and function from a link test using a media converter designed to convert from one type of media to another with a missing-link function.
As described before, since a conventional media converter is set to the test mode by operating the link-test switch, it is impossible to activate the link test from cable side (unshielded twisted pair (UTP) cable or fiber-optic cable) and therefore difficult to perform the link test rapidly and easily. In other words, the conventional media converter is not designed to be controlled from network side due to its property.
When the missing-link function of media converter is activated, the host computer cannot monitor any status of the media converter, even if the media converter operates normally. Accordingly, when some failure occurs in the link through the media converter, the host cannot specify where a failure has occurred, in the link from the host to the media converter, in the media converter itself, or in the link away from the media converter.